1. Field of the Invention
The invention relates to a scheme for grounding a printed circuit board to a frame of an electronic system, and more particularly to a grounding scheme in which a concealed biaxial spring is used to provide electrical contact between a grounding pad on the printed circuit board and a standoff used to mount the printed circuit board to the frame of the electronic system.
2. Background Information
The integration of printed circuit boards into electronic systems, such as servers, requires that the boards be mechanically fastened and electrically grounded to the system frame, usually accomplished by securing the boards to the frame with screws. These screws provide a ground path from the boards to the frame and electrically carry the ground from the contact pads, which are wired to the ground planes on the boards, to the sheet metal of the frame. However, there are disadvantages to this type of design.
In the above-described arrangement, time is required to install the necessary screws through the board into the system frame. It also requires adequate space to access the screws with a tool. In addition to the screw space constraint, the location of ground pads dictates where the printed circuit board assembly must be mechanically fastened and electrically grounded. In some applications, these desired locations might reside under a part that is secured to the printed circuit board assembly, making it impossible to install the board assembly using screws. Thus, there is a need for a toolless arrangement for fastening and grounding printed circuit boards in such situations. There is further a need of a toolless arrangement that solves the problem of space and access constraints faced by conventional fasteners, such as screws, and also helps reduce board installation time while still providing an adequate grounding scheme.
It is, therefore, a principle object of this invention to provide a concealed biaxial card to frame grounding scheme.
It is another object of the invention to provide a concealed biaxial card to frame grounding scheme that solves the above-mentioned problems.
These and other objects of the present invention are accomplished by the concealed biaxial card to frame grounding scheme disclosed herein.
In an exemplary aspect of the invention, a board assembly is mounted and secured to a plurality of standoffs attached to the frame of an electronic system. The assembly includes a printed circuit board having a grounding pad formed on one side, and a conductive spring compressible along two axes that makes contact with both the grounding pad and one of the standoffs when the printed circuit board is mounted and secured to the standoffs. The conductive spring completes a ground path from the printed circuit board to the system frame through the one standoff. In the preferred embodiment, the printed circuit board is attached to a plastic stiffener that includes means for retaining the conductive spring in position. Preferably the retaining means is a boss formed on the stiffener and the conductive spring is formed with a hole that fits over the boss, so that no additional hardware is required to retain the conductive spring. The conductive spring has two portions, with the hole being between them. The first portion is adapted to exert a first spring force in a first direction along one axis, and the second portion is adapted to independently exert a second spring force in a second direction along another axis that is essentially perpendicular to the first axis. When the printed circuit board is attached to the stiffener, the conductive spring is concealed and captivated between them.
In another exemplary aspect of the invention, the printed circuit board has a securing means proximate to the grounding pad for securing, without the use of tools, the printed circuit board to the one standoff with which the conductive spring makes contact. The securing means is preferably a keyhole shaped hole in the printed circuit board that has a circular portion and a slotted portion, the slotted portion having a width less than a diameter of the circular portion. The end of the corresponding standoff has a head with a diameter less than the diameter of the circular portion of the keyhole and greater than the width of the slotted portion. When the printed circuit board is lowered onto the standoffs, the head of the one standoff passes through the circular portion of the keyhole. To secure the printed circuit board, it is slid into a position such that the head is over the slotted portion of the keyhole. In this position, the conductive spring presses against and makes contact with the one standoff, thus completing the electrical path from the board ground to the system frame.
In yet another aspect of the invention, the printed circuit board is locked in place in its secured position, preferably by using fasteners in at least two places to fasten the printed circuit board to the plurality of standoffs.
The concealed biaxial card to frame grounding scheme described herein advantageously reduces the time required to fasten and ground the printed circuit board, as well as creating a solution that requires only two locations where space for a tool is a consideration.